The least to be said that is that we have some novelty here with the light inside the lens, very attractive concept for a macro really tempting, only disadvantage you have to be very close to your subject.
Dentists should love this lens
To have more options, to be more creative when it comes to pics witha wide-open lens, to use lower ISO ... it's always better to have a fast lens ...
This is very much a macro lens first, and a general purpose prime second. Most macro users don't care much about using the lens wide open as lack of depth of field is often a problem. DSLR macro lenses tended to be f/2.8 as that was needed to maintain phase AF, as they were effective f/5.6 at 1x magnification (not sure how the 180mm f/3.5L gets around that). Contrast AF wouldn't have that limitation, although the possible hit to any phase AF on sensor might result in slower AF.
<a class="bbc_url" href="http://snowporing.deviantart.com/">dA</a> Canon 7D2, 7D, 5D2, 600D, 450D, 300D IR modified, 1D, EF-S 10-18, 15-85, EF 35/2, 85/1.8, 135/2, 70-300L, 100-400L, MP-E65, Zeiss 2/50, Sigma 150 macro, 120-300/2.8, Samyang 8mm fisheye, Olympus E-P1, Panasonic 20/1.7, Sony HX9V, Fuji X100.